It is currently thought that infant pain remains undertreated due to a lack in knowledge concerning valid indicators of pain in infants that are requisite for the accurate assessment of infant pain. The general purpose of this research is to explicate age-appropriate models of infant pain which can be used as a basis for the development of a clinical tool(s) to improve nursing assessment of infant pain. Enhanced assessment will facilitate improved pain management for infants. A multimethod, multiple modality approach will be utilized to do this. Ethologically described visible infant behaviors, vocal measures, physiological and certain acoustic measures of stress-arousal, cues nurses report using infant pain assessment, and nurse-assessed levels of pain will be obtained for 80 study infants. These will be fully described and interrelationships among them explored. Five specific aims guide the attainment of this overall purpose. 1) To describe the following variables within each of the assessed levels of pain for infants in four age categories: a) infant background variables, b) ethnographically derived assessment cues/patterns of cues reported by pediatric nurses, c) ethologically derived vocal and visible behavioral variables, d) vocal and physiological variables suggestive of stress- arousal. 2) To elucidate assessment cues by: (a) describing how cues and/or cue patterns in Aim 1b are selected, organized, weighted and otherwise used in making a nursing assessment about the level of pain experienced by infants; (b) identifying specific elements of any global cues through a combination of ethological and ethnographic analyses; and (c) describing the similarities and differences in cues, cue-patterns, global cue elements and their organization both across nurses and across infants with different levels of assessed pain and in the different age categories. 3) To identify patterns of similarities and differences of ethologically derived variables across infants of similar and different ages and assessed levels of pain. 4) To examine the interrelatedness of the following within and across age categories of infants: (a) infant background variables; (b) vocal and physiological variables associated with stress arousal; and (e) assessed 1c and 3; (d) vocal and physiological variables associated with stress arousal; and (e) assessed level-of-pain ratings. 5) Using the results of all qualitative and quantitative analyses, to construct a model(s) that can be used to develop a refined clinical tool to improve nursing assessment of infant pain.